Apremilast, i.e. N-[2-[(1S)-1-(3-ethoxy-4-methoxyphenyl)-2-(methylsulfonyl)ethyl]-1,3-dioxo-2,3-dihydro-1H-isoindol-4-yl]acetamide), also referred to herein as “APM”, has the following chemical formula, wherein “S”, if not connected via a chemical bond in the formula, denotes the S-form of the chiral center.

Apremilast is a phosphodiesterase 4 inhibitor and blocks the action of an enzyme inside cells called phosphodiesterase 4 (PDE4). This enzyme plays a role in triggering the production of messenger molecules in the immune system called cytokines, which are involved in inflammation and other processes that cause psoriasis and psoriatic arthritis. By blocking PDE4, Apremilast reduces the level of these cytokines in the body, and so reduces the inflammation and other symptoms of psoriasis and psoriatic arthritis. Apremilast is the active ingredient of the medicament Otezla®, distributed by Celgene, Ltd, for the treatment of adults with psoriatic arthritis (inflammation of the joints associated with psoriasis) and moderate to severe plaque psoriasis (a disease causing red, scaly patches on the skin).
EP2276483 B1 discloses various polymorphic forms of Apremilast, i.e. Forms A, B, C, D, E, F and G. Regarding the characterization of these Forms A, B, C, D, E, F and G, in particular their XRPD peak locations and intensity, reference is made to EP2276483 B1. The stability, interconversion and equilibration studies in EP2276483 B1 show that most of these crystalline forms have a high tendency of interconversion, i.e. one polymorphic form converts into another polymorphic form in the presence of solvents.